Semiconductor laser diode module

ABSTRACT

A semiconductor laser diode module in which a laser diode and an optical fiber are optically coupled with each other efficiently irrespective of an ambient temperature change within the laser diode module. The laser diode module includes a laser diode, an optical system including an optical fiber and a lens portion, a holder configured to receive a portion of the optical system, a base having a holder mounting member and a fastening member, and a bottom plate configured to support the base. The holder is mounted to the fastening member at a first joint position, and the fastening member is mounted to the holder mounting member at a second joint position, where the first and second joint positions are located at substantially a same distance from the bottom plate. Alternatively, the first and second joint positions are coplanar with an active layer of the diode. Alternatively, the holder is mounted to the fastening member at a plurality of first joint positions, and the fastening member being mounted to the holder mounting member at a plurality of second joint positions, where the plurality of first and second joint positions are coplanar.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor laser diodemodule used in the field of optical communications.

[0003] 2. Discussion of the Background

[0004] With the explosive growth of the Internet and othercommunications needs, there has developed a commensurate need fortransmission systems to handle the ever increasing demand for capacityto transmit signals. Fiber optic systems have become the technology ofchoice for meeting this demand. Significant attention has been directedto systems which use dense wavelength division multiplexing (DWDM) toincrease the number of signal channels that can be transmitted through asingle optical fiber.

[0005] Semiconductor laser diodes have been used as a pumping lightsource for optical fiber amplifiers and as a signal light source in thefiber optic systems. The semiconductor laser diode module is a device inwhich a laser beam from the semiconductor laser diode is opticallycoupled with an optical fiber.

[0006] Erbium doped fiber amplifiers require 980 nm band and 1480 nmband semiconductor laser diode modules as pumping light sources. AndRaman amplifiers require 1350-1540 nm band semiconductor laser diodemodules as pumping light sources. 1550 nm band semiconductor laser diodemodules are well-known as the signal light source.

[0007] Optical coupling system between the laser diode and the opticalfiber is selected depending on a laser diode chip structure, the shapeof the mode-field of the light emitted from laser diode, and so on, toget higher optical coupling efficiency thereby.

[0008] The semiconductor laser diode module is required to have acertain quality of optical characteristics even at a higher ambienttemperature. The optical characteristics are represented by thestability of the optical coupling efficiency between laser diode and theoptical fiber, the stability of the output power from laser diode, andthe monitor current.

SUMMARY OF THE INVENTION

[0009] The present invention advantageously provides a laser diodemodule in which a laser diode and an optical fiber are optically coupledwith each other efficiently irrespective of an ambient temperaturechange.

[0010] A first aspect of the present invention advantageously provides alaser diode module that includes a laser diode, an optical systemincluding an optical fiber and a lens portion, a holder configured toreceive a portion of the optical system, a base having a holder mountingmember and a fastening member, and a bottom plate configured to supportthe base. The optical system is configured to receive and transmit abeam emitted from the laser diode through the lens portion to theoptical fiber along an optical axis. The holder is mounted to thefastening member at a first joint position, and the fastening member ismounted to the holder mounting member at a second joint position, wherethe first joint position and the second joint position are located atsubstantially a same distance from the bottom plate.

[0011] A second aspect of the present invention advantageously providesa laser diode module that includes a laser diode having an active layer,an optical system including an optical fiber and a lens portion, aholder configured to receive a portion of the optical system, and a basehaving a holder mounting member and a fastening member. The opticalsystem is configured to receive and transmit a beam emitted from thelaser diode through the lens portion to the optical fiber along anoptical axis. The holder is mounted to the fastening member at a firstjoint position, and the fastening member is mounted to the holdermounting member at a second joint position, where the first jointposition and the second joint position are coplanar with the activelayer of the diode.

[0012] A third aspect of the present invention advantageously provides alaser diode module that includes a laser diode, an optical systemincluding an optical fiber and a lens portion, a holder configured toreceive a portion of the optical system, and a base having a holdermounting member and a fastening member. The optical system is configuredto receive and transmit a beam emitted from the laser diode through thelens portion to the optical fiber along an optical axis. The holder ismounted to the fastening member at a plurality of first joint positions,and the fastening member being mounted to the holder mounting member ata plurality of second joint positions, where the plurality of firstjoint positions and the plurality of second joint positions arecoplanar.

[0013] A fourth aspect of the present invention advantageously providesa semiconductor laser diode module that includes a laser diode, anoptical system including an optical fiber and a lens portion, a holderconfigured to receive a portion of the optical system, a fastening meansfor fixing the portion of the optical system by supporting and clampingthe holder on sides thereof, a base configured to support the fasteningmeans and the laser diode, and a bottom plate configured to support thebase, the fastening means, the holder, the optical system, and the laserdiode. The optical system is configured to receive and transmit a beamemitted from the laser diode through the lens portion to the opticalfiber along an optical axis, and the base includes a fastening meansmounting member configured to mount the fastening means. A first weldingposition is obtained by welding the fastening means to the fasteningmeans mounting member and a second welding position is obtained bywelding the fastening means and the holder, where the first weldingposition and the second welding position are at substantially a sameheight in a direction perpendicular to the bottom plate.

[0014] The present invention provides, for example, a semiconductorlaser diode module having a holder configured to receive a portion ofthe optical system, and a base having a holder mounting member and afastening member. The holder is mounted to the fastening member at afirst joint position, and the fastening member is mounted to the holdermounting member at a second joint position, where the first jointposition and the second joint position are located at substantially asame distance from the bottom plate. The orientation of the jointpositions at a same distance from the bottom plate prevents any warpingcaused during the manufacturing of the joints and ensures that anyexpansion during heating will occur in a uniform manner without warping.Accordingly, the configuration of the present invention suppresses thedegradation in optical coupling efficiency between the laser diode andthe optical fiber due to the temperature change of the environmentalconditions of the semiconductor laser diode module.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] A more complete appreciation of the invention and many of theattendant advantages thereof will become readily apparent with referenceto the following detailed description, particularly when considered inconjunction with the accompanying drawings, in which:

[0016]FIG. 1 is a cross-sectional view of a semiconductor laser diodemodule according to a first embodiment of the present invention;

[0017]FIG. 2 is a perspective view of the internal components of thefirst embodiment of the semiconductor laser diode module according tothe present invention;

[0018]FIG. 3 is a top view of the internal components of the firstembodiment of the semiconductor laser diode module according to thepresent invention;

[0019]FIG. 4 is an exploded, perspective view of a base of the firstembodiment of the semiconductor laser diode module according to thepresent invention;

[0020]FIG. 5 is a cross-sectional view of a holder mounting member ofthe first embodiment of the semiconductor laser diode module accordingto the present invention taken along line V-V in FIG. 4;

[0021] FIGS. 6(a), 6(b), 6(c), and 6(d) are perspective views ofalternative embodiments of fastening members of the first embodiment ofthe semiconductor laser diode module according to the present invention;

[0022] FIGS. 7(a) and 7(b) are side and top views, respectively, of alens portion of an optical fiber of the first embodiment of thesemiconductor laser diode module according to the present invention;

[0023] FIGS. 8(a) and 8(b) are perspective views of an arrangementregion of a laser diode and an arrangement region of a monitor photodiode, respectively, of the first embodiment of the semiconductor laserdiode module according to the present invention;

[0024]FIG. 9 is a perspective view of the internal components of asecond embodiment of the semiconductor laser diode module according tothe present invention;

[0025]FIG. 10 is a plan view of the internal components of the secondembodiment of the semiconductor laser diode module according to thepresent invention;

[0026]FIG. 11 is an exploded, perspective view of a base of the secondembodiment of the semiconductor laser diode module according to thepresent invention;

[0027] FIGS. 12(a) and 12(b) are cross-sectional, partial views of arelated art semiconductor laser diode module depicted in a non-operatingstate in FIG. 12(a), and in a operating state in FIG. 12(b) where themodule is depicted as being warped;

[0028] FIGS. 13(a) and 13(b) are schematic representations of therelated art semiconductor laser diode module depicting a non-operatingstate in FIG. 13(a), and an enlarged view of a portion of FIG. 13(a)depicting an optical coupling of the laser diode and optical fiber inFIG. 13(b);

[0029] FIGS. 14(a) and 14(b) are schematic representations of therelated art semiconductor laser diode module depicting a operating statein FIG. 14(a), and an enlarged view of a portion of FIG. 14(a) depictingan optical coupling of the laser diode and optical fiber in FIG. 14(b)where the non-operating state is depicted in phantom lines forcomparison;

[0030]FIG. 15 is a chart representing monitor tracking error based uponambient temperature changes in the related art semiconductor laser diodemodule and the semiconductor laser diode module according to the presentinvention;

[0031]FIG. 16 is an enlarged, schematic side view of a laser diode andan optical fiber according to the first embodiment of the semiconductorlaser diode module according to the present invention;

[0032]FIG. 17 is a perspective view of the internal components of athird embodiment of the semiconductor laser diode module according tothe present invention;

[0033]FIG. 18 is a cross-sectional view of the semiconductor laser diodemodule according to the third embodiment of the present invention;

[0034]FIG. 19 is an exploded, perspective view of a base of the thirdembodiment of the semiconductor laser module according to the presentinvention;

[0035]FIG. 20 is a cross-sectional view of a holder mounting member ofthe third embodiment of the semiconductor laser diode module accordingto the present invention taken along line XIX-XIX in FIG. 19;

[0036]FIG. 21 is a cross-sectional view of the internal components ofthe third embodiment of the semiconductor laser diode module accordingto the present invention taken along line XX-XX in FIG. 17;

[0037]FIG. 22 is a cross-sectional view of a semiconductor laser diodemodule according to a fourth embodiment of the present invention;

[0038]FIG. 23 is a top view of a conceptual arrangement between a laserdiode, a lens portion and a structural support member of the presentinvention; and

[0039] FIGS. 24 (a) and (b) are side and top views of an alternativeembodiment of a lens portion of an optical fiber according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

[0040] Description of the Art for Comparison

[0041]FIG. 12(a) depicts an example of a structure of a relatedsemiconductor laser diode module for comparison. The semiconductor laserdiode module depicted in FIG. 12(a) has a laser diode 1 for emitting alaser beam. The laser diode module includes an optical fiber 4 having alens portion 14 provided opposite a laser beam emitting end surface 31of the laser diode 1. The optical fiber 4 is accommodated in a sleeve 3made of metal. The optical fiber 4 receives and transmits the beamemitted from the laser diode 1 through the lens portion 14. The lensportion 14 has a wedge-shape.

[0042] The sleeve 3 is supported by fastening members 6 and 7, which aremounted on a base 2. The fastening members 6 and 7 are configured tosupport the optical fiber 4 through the sleeve 3 at intervals in alongitudinal direction of the optical fiber 4. The laser diode 1 ismounted on and fixed to laser diode bonding portion 21 on the base 2through a heat sink 22. A monitor photo diode 9 is mounted through amonitor photo diode carrier 39 to the base 2. The monitor photo diode 9monitors the optical output power of the laser diode 1. The base 2 ismounted on a thermo module 25.

[0043] The thermo module 25, the base 2, the laser diode 1, the opticalfiber 4 and the fastening members 6 and 7 are accommodated in a package27. The thermo module 25 is mounted on a bottom plate 26 of the package27. The bottom plate 26 of the package 27 is formed of a Cu—W alloy,specifically CuW20 (20% of Cu, 80% of W by weight). The thermo module 25has a base side plate member 17, a bottom plate side plate member 18,and peltier elements 19 clamped between the plate members 17 and 18. Thebase side plate member 17 and the bottom plate side plate member 18 ofthe thermo module 25 are both made of Al₂O₃.

[0044] The fastening members 6 and 7 and the base 2 are welded togetherby a known welding method, such as YAG welding using a YAG laser, atlaser welding portions 10, and the fastening members 6 and 7 and thesleeve 3 are welded together at laser welding portions 11. The laserwelding portions 11 are formed at a higher position in a Y-direction inFIGS. 12(a) and 12(b) than that of the welding portions 10.

[0045] In the above-described semiconductor laser diode module, theoptical fiber 4 is aligned to the laser diode 1 so that the laser beamemitted from the laser diode 1 is received and transmitted in theoptical fiber 4 for use as desired. Also, in the semiconductor laserdiode module, when current for driving the laser diode 1 is turned on,the temperature of the laser diode 1 is increased by heat generationcaused by the current. The increase in temperature changes an opticaloutput power of the laser diode 1. Accordingly, during the operation ofthe semiconductor laser diode module, the temperature of the laser diode1 is monitored by a thermistor (not shown) fixed in the vicinity of thelaser diode 1, and the thermo module 25 is operated on the basis of themeasured temperature value. The thermo module 25 is operated such thatthe current through the thermo module 25 is controlled in an effort tomaintain a constant temperature of the laser diode 1 to keep the opticaloutput power of laser diode constant.

[0046] The inventors of the present invention have identified a problemwith the above-described semiconductor laser diode module. Theabove-described semiconductor laser diode module is configured such thatthe second laser welding portion 11 fixing together the sleeve 3 and thefastening members 6 and 7 is formed at a level higher by about 1600 μmin a height direction (the Y-direction in FIG. 12(a)) than the firstlaser welding portion 10 fixing together the fastening members 6 and 7and the base 2. Accordingly, when the flexure of the base 2 isgenerated, the sleeve 3 is significantly displaced about a pivot pointat the first laser welding portion 10, thereby enhancing the degradationof the optical coupling efficiency between the laser diode 1 and theoptical fiber 4.

[0047] If the optical coupling efficiency between the laser diode 1 andthe optical fiber 4 is degraded in accordance with a change in ambienttemperature, then the light intensity of the beam received andtransmitted by the optical fiber 4 decreases, and it becomes impossibleto suitably operate the optical communication system to which thesemiconductor laser diode module is applied.

[0048] The inventors conducted a test on a semiconductor laser diodemodule as described above, and determined that a change in ambienttemperature causes warping of the base, which in turn causes an end ofthe optical fiber to shift with respect to the laser diode. FIGS. 13(a)and 13(b) are schematic representations of such a semiconductor laserdiode module depicting a lower ambient temperature state, i.e. 25° C.(room temperature) in FIG. 13(a), and an enlarged view of a portion ofFIG. 13(a) depicting an optical coupling of the laser diode and opticalfiber in FIG. 13(b). FIGS. 14(a) and 14(b) are schematic representationsof the semiconductor laser diode module of FIGS. 13(a) and 13(b)depicted in a higher ambient temperature state, i.e. 85° C. in FIG.14(a), and an enlarged view of a portion of FIG. 14(a) depicting anoptical coupling of the laser diode and optical fiber in FIG. 14(b). InFIG. 14(b), the configuration of FIG. 13(b) is depicted in phantom linesfor comparison.

[0049] As depicted in FIG. 13(b), in the lower ambient temperaturestate, the laser diode is a distance d₁ from the lens portion of theoptical fiber. As depicted in FIG. 14(b), in the higher ambienttemperature state the module warps such that the laser diode is adistance d₂ from the lens portion of the optical fiber. The change ofthe distance from d₁ to d₂ become longer, then the stability of opticalcharacteristics, for example, the stability of the optical couplingefficiency between laser diode and optical fiber, the stability ofoutput power from laser diode, and the stability of the monitor current,are more reduced. It is necessary to suppress the warping of the base soas to minimize the change of distance d₁ and d₂ for improvement of theseoptical characteristics.

[0050] Description of the Preferred Embodiments of the Invention

[0051] The present invention will now be described with reference topreferred embodiments that provide advantageous structures that overcomeproblems identified by the inventors, which are described above. In thedetailed description of the embodiments, the same reference numeralswill be used to indicate the same or similar components and a duplicatedexplanation will be omitted.

[0052] Referring now to the drawings, FIGS. 1-8(b) depict asemiconductor laser diode module according to a first embodiment of thepresent invention. As depicted in FIG. 1, the semiconductor laser diodemodule includes a package 27 configured to accommodate a laser diode 1,an optical fiber 4 having a lens portion 14, a sleeve or ferrule (ormore generally a holder) 3 for receiving therein the optical fiber 4, atleast one fastening means or fastening members 6 and 7 (7 a, 7 b) forsupporting the optical fiber 4 through the sleeve 3, a base 2 on whichthe fastening members 6 and 7 and the laser diode 1 are mounted directlyor indirectly, and a thermo module 25.

[0053] The base 2 according to the first embodiment is advantageouslyprovided with a laser diode mounting member 8 on which the laser diode 1is to be mounted, and a fastening means mounting member or holdermounting member 5 on which the fastening members 6 and 7 are to bemounted. The laser diode mounting member 8 is arranged on the thermomodule 25 in contact therewith, and as depicted in FIGS. 1, 2 and 4. Thelaser diode mounting member 8 has an upper portion with a laser diodebonding portion 21 formed integrally therewith, which defines a laserdiode mounting region. The holder mounting member 5 is disposed in aposition that does not interfere with the laser diode mounting region ofthe laser diode mounting member 8.

[0054]FIG. 4 is an exploded, perspective view of the base 2 includingthe holder mounting member 5 and the laser diode mounting member 8. Theholder mounting member 5 is fixed on an upper surface of the laser diodemounting member 8 on a brazing bonding portion 46 indicated by thehatching in FIG. 4. Note that in the preferred embodiment, portions ofthe holder mounting member 5 extend alongside the laser diode bondingportion 21.

[0055] The base 2 of the present invention is constructed of a laserdiode mounting member 8 that is advantageously formed of material havinga thermal expansion coefficient in a range between a thermal expansioncoefficient of the holder mounting member 5 and a thermal expansioncoefficient of a base side plate member 17 of the thermo module 25. Forexample, the laser diode mounting member 8 is preferably formed of aCu-W alloy, such as CuW10 (Cu of 10%, W of 90% by weight), having athermal expansion coefficient of about 6.5×10⁻⁶. Further, the holdermounting member 5 is preferably formed of an Fe-Ni-Co alloy, such asKovar®, having a thermal expansion coefficient in a range from 4.5×10⁻⁶to 5.1×10⁻⁶, and the base side plate member 17 of the thermo module 25is preferably formed of a material such as Al₂O₃, having a thermalexpansion coefficient of about 6.7×10⁻⁶.

[0056] During operation of the first embodiment of the laser diodemodule, a light beam is emitted from the laser diode 1 and is receivedand transmitted by the optical fiber 4. The thermo module 25 controlsthe temperature of the laser diode 1 during the operation of the laserdiode 1. In the present invention, the laser diode mounting member 8,which is in contact with the base side plate member 17 of the thermomodule 25, is advantageously made of material having a thermal expansioncoefficient in the range between the thermal expansion coefficient ofthe holder mounting member 5 provided on the upper side thereof and thethermal expansion coefficient of the base side plate member 17 (i.e., inthe present embodiment, CuW10 having the thermal expansion coefficientbetween that of Kovar® and that of Al₂O₃). By comparison, in the relatedart embodiment depicted in FIG. 12(a), the base 2, which is made ofmaterial having a low thermal expansion such as Kovar®, directlycontacts and the plate member 17 of the thermo module 25, which is madeof a material having a high thermal expansion coefficient such a Al₂O₃.Since the thermal expansion coefficients of adjacent contacting materialin the present invention gradually increase, rather than substantiallyincreasing, as in the related art embodiment. The gradual increase inthe thermal expansion coefficients of adjacent contacting material inthe present invention reduces the warping or flexure of the base 2generated due to the temperature gradients created during operation ofthe laser diode. Accordingly, the present invention provides a structurethat suppresses the degradation in the optical coupling efficiencybetween the laser diode 1 and the optical fiber 4 due to the ambienttemperature change during operation of the laser diode module.

[0057] The present invention advantageously preferably provides that thethermal expansion coefficient of the laser diode mounting member 8 isequal to the thermal expansion coefficient of the bottom plate 26 of thepackage 27. For example, both the laser diode mounting member 8 and thebottom plate are preferably formed of a Cu—W alloy, such as CuW10.Accordingly, the same magnitude of stress is applied to both upper andlower sides of the thermo module 25 when the temperature change of thesemiconductor laser diode module is generated. Thus, the warping of thethermo module 25 is offset. Accordingly, the present invention providesa structure that effectively suppresses the degradation of the opticalcoupling efficiency between the laser diode 1 and the optical fiber 4due to an ambient temperature change.

[0058] The sleeve 3, the fastening members 6 and 7, and the holdermounting member 5 are preferably joined together by laser welding. It istherefore preferable to construct the sleeve 3, the fastening members 6and 7, and the holder mounting member 5 of a material that has lowthermal conductivity and a low thermal expansion coefficient, andtherefore has superior weldability, such as Kovar®. Additionally, theholder mounting member 5 is preferably made of a material havingsubstantially the same thermal expansion coefficient as that of theoptical fiber 4 and sleeve 3 in order to reduce any adverse effects onthe optical fiber 4 due to a difference in thermal expansioncoefficients. Accordingly, the present invention provides asemiconductor laser diode module that is easy to manufacture.

[0059] Additionally, in the present invention, the thermal conductivityof the laser diode mounting member 8 is advantageously preferably largerthan the thermal conductivity of the holder mounting member 5. Such aconfiguration provides an advantageous thermal heat path from the laserdiode 1 through the heat sink 22 and through the laser diode mountingmember 8 (without insulation from the holder mounting member 5) to thethermo module 25 and to the bottom plate 26, thereby providing for theefficient transfer of heat away from the laser diode 1 during operation.For example, as noted above, the laser diode mounting member 8 ispreferably formed of a Cu—W alloy, such as CuW10, and the holdermounting member 5 is preferably formed of an Fe—Ni—Co alloy, such asKovar®. The thermal conductivity of CuW10 is in the range of about 180to 200 W/mK, which is about ten times greater than the thermalconductivity of Kovar®, which is in the range of about 17 to 18 W/mK.

[0060] Accordingly, the present invention provides a heat pathconfiguration through the laser diode mounting member 8 of the base thatefficiently controls the temperature of the laser diode 1 using thethermo module 25, thereby allowing the laser diode 1 to operate at full,optimal power without the risk of overheating. The configuration of thepresent invention reduces the power consumption of the laser diodemodule as compared to the related art embodiment, since it allows thelaser diode 1 to operate at optimal power and allows the thermo module25 to efficiently transfer heat away from the laser diode withoutinsulation interference from the holder mounting member. Accordingly,the present invention advantageously provides a semiconductor laserdiode module that has small power consumption. Furthermore, the holdermounting member 5 of the present invention does not reach hightemperatures, as did the entire base of the related art module, andtherefore the overall warping of the base is reduced.

[0061] The holder mounting member 5 of the base 2 is provided togenerally extend in a longitudinal direction of the optical fiber 4 froman end portion on an optical fiber mounting side of the thermo module 25(i.e., at the right side of the thermo module 25 as depicted FIG. 1).Further, the holder mounting member 5 is provided on an upper surface ofthe laser diode mounting member 8. Additionally, the sleeve 3 holdingthe optical fiber 4 is fixed to the holder mounting member 5 andprojects from the end portion on the optical fiber mounting side of thethermo module 25. In this configuration, the projecting portion of theholder mounting member 5 is out of contact with the thenno module 25 andtherefore is not subjected to warping effects from the thermo module 25.Furthermore, since the sleeve 3 is fixed to the holder mounting member 5and projects from the thermo module 25, then the sleeve 3 is notsubjected to warping effects from the thermo module 25, thereby furthereffectively suppressing the reduction in optical coupling efficiencybetween the laser diode 1 and the optical fiber 4.

[0062] It should be noted that if the projection length L (see FIG. 1)of the holder mounting member 5 is too long, the bonding strength to thelaser diode mounting member 8 may be insufficient due to the weight ofthe projecting portion of the projection length L. Accordingly, there isa possibility that the bonding would be released if the projectingportion is subjected to vibration. Therefore, it is preferable toestablish a configuration where L≦5 mm.

[0063] As depicted in FIG. 2, the laser diode mounting member 8preferably has a reinforcement portion 20 that extends under theprojecting portion of the holder mounting member, and further preferablyextends under the fastening member 6 located closer to the laser diode1. In the first embodiment, the reinforcement portion 20 has arectangular-parallelepiped shape. The reinforcement portion 20 supportsand braces the holder mounting member 5, whereby if vibration is appliedto the holder mounting member 5 in the Y-direction, then the effects ofthe vibration will be shifted to the laser diode mounting member 8. Sucha configuration will prevent vibration from adversely effecting theoptical coupling between the laser diode 1 and the optical fiber 4.Additionally, it is noted that the contact area between the holdermounting member 5 and the laser diode mounting member 8 can be increasedso that both components are more firmly and more mechanically fixedtogether. Furthermore, it should be noted that since the lower surfaceof the reinforcement portion 20 is out of contact with the thermo module25, then the reinforcement portion 20 is free from the adverse effectsof the warping of the thermo module 25.

[0064] As depicted in FIGS. 1 through 3, the fastening members 6 and 7are joined to the holder mounting member 5 at first joint portions orpositions 10, which are preferably formed using laser-weldingtechniques. The sleeve 3 is joined to the fastening members 6 and 7 atsecond joint portions or positions 11 (11 a, 11 b), which are alsopreferably formed using laserwelding techniques. The holder mountingmember 5 is used to support the fastening members 6 and 7, and thefastening members 6 and 7 are used to support the sleeve 3 and therebysupport the optical fiber 4. It should be noted that when the holdermounting member 5 and the fastening members 6 and 7 are welded togetherby laser beams, if the top surface of the holder mounting member 5 isflush with the top surface of the fastening members 6 and 7 (within ±100μm), it is possible to readily keep constant the height of the laserwelding portions 10 for every product. FIG. 16 is an enlarged, schematicside view of a laser diode and an optical fiber according to the firstembodiment of the semiconductor laser diode module depicting first jointpositions 10 and a second joint position 11.

[0065] The first joint positions 10 and the second joint positions 11are preferably located at substantially a same distance from the bottomplate 26. Preferably, the first joint positions 10 and the second jointpositions 11 are at substantially a same height in a directionperpendicular to the bottom plate 26, with a tolerance for a differencein height therebetween of within ±500 μm and more preferably within ±50μm. Preferably, the first joint positions 10 and the second jointpositions 11 are coplanar with the active layer of the laser diode 1,for example, the height of the first and second joint positions 10 and11 are at substantially the same height as the ridge line 14 a(refer toFIGS. 7(a),7(b)) of the optical fiber 4 which is opposite the activelayer of the laser diode 1.

[0066] The present invention advantageously provides at least one firstjoint position 10 joining the holder mounting member 5 of the base 2 andthe fastening members 6 and 7 of the optical fiber receiving sleeve 3,and at least one second joint position 11 joining the fastening members6 and 7 and the sleeve 3, where the first and second joint positions areformed to be at substantially the same height level in the directionperpendicular to the package bottom plate 26. Accordingly, even if thebase 2 is warped slightly, there is little possibility that the sleeve 3would be displaced about the pivot of the first joint position 10 due tothis warping. It is therefore possible to effectively suppress thedegradation of the optical coupling efficiency between the laser diode 1and the optical fiber 4.

[0067] In the first embodiment as depicted in FIGS. 3 and 5, at leastone structural support member or warping preventing means 15 is formedalong a longitudinal direction of the optical fiber 4 in the holdermounting member 5 of the base 2. The structural support member 15functions to prevent the warping of the base 2 by providing a portionhaving a thickness that provides structural integrity to the base 2. Inthis embodiment, the structural support member 15 is formed as a wallportion extending in a longitudinal direction of the optical fiber 4 andprovided upright on at least the upper side of a bottom portion 16 ofthe holder mounting member 5, as depicted in FIG. 5. In the firstembodiment, the structural support members 15 are formed integrally withthe holder mounting member 5. Therefore, there is no degradation inmechanical strength due to the connection between the structural supportmembers 15 and the holder mounting member 5, as compared with anembodiment where the structural support members 15 and the holdermounting member 5 are discretely formed to be adhered together.

[0068] The first embodiment advantageously includes a structural supportmember that extends along the longitudinal direction (Z-direction inFIG. 1) of the holder mounting member 5. Preferably, the structuralsupport member 15 is provided over a full region along the longitudinaldirection of the holder mounting member 5 (the region within the framesB indicated by the dotted lines in FIG. 3). Additionally, the structuralsupport member 15 is preferably formed on both sides of the holdermounting member 5 symmetrically about an optical axis of the opticalfiber 4, a portion 33 of the optical axis being depicted in FIG. 3 asextending to connect the laser beam emitting facet 31 of the laser diode1 and a laser beam receiving end 32 of the optical fiber 4. Thestructural support member 15 preferably includes portions that areformed on both sides of the fastening member 6 located closer to thelaser diode 1. Tip end portions of the structural support member 15extend to the region adjacent to the laser diode bonding portion 21 ofthe laser diode mounting member 8, such that the tip end portions areprovided on both sides of the laser diode bonding portion 21. The tipend portions adjacent the laser diode bonding portion 21 providerigidity to the region between the laser diode 1 and the optical fiber4, thereby maintaining efficient optical coupling. Therefore, thewarping of the base 2 in the region where the axial portion 33 and thefastening member 6 are arranged is effectively suppressed. The firstembodiment of the present invention thus effectively suppresses thewarping of the base 2 due to a temperature change during operation ofthe semiconductor laser diode module, thereby effectively suppressingdegradation in the optical coupling efficiency between the laser diode 1and the optical fiber 4.

[0069] As depicted in FIGS. 3 and 4, the holder mounting member 5includes fitting recess portions 37 for receiving the fastening members6 and 7. The fitting recess portions 37 are defined by the wall portionsconstituting the structural support members 15 and the wall portions 35for fastening the sides of the fastening members 6 and 7. The fasteningmembers 6 and 7 are welded and fixed at the first joint positions 10,such that the fastening members 6 and 7 are received within the fittingrecess portions 37. Incidentally, in the first embodiment, the wallportions 35 are part of the structural support members 15 and thereforeconstituting a warping preventing means. The wall portions 35 can beintegrally formed on the holder mounting member 5 by, for example,cutting away the fitting recess portions 37 for receiving the fasteningmembers 6 and 7 and an insertion portion for inserting the sleeve 3, asin the configuration depicted in FIG. 4.

[0070] The holder mounting member 5 has a U-shaped cross-sectional areataken along a plane transverse to the optical axis of the optical fiber,as depicted in FIG. 5. The structural support members 15 provide theside walls of the U-shaped cross-sectional area, and give the holdermounting member 5 structural integrity that prevents the warping of theholder mounting member 5. Alternatively, the holder mounting member 5can be formed with a different cross-sectional shape, such as anH-shape, etc.

[0071] Wall portions 35 extended to the laser diode side and the laserdiode bonding portion 21 also form together the U-shaped cross-sectionalarea around the laser diode 1 together.

[0072] As depicted in FIGS. 2 and 3, the fastening members 6 and 7 areseparated to support the sleeve 3 and the optical fiber 4 at differentpositions at intervals along the longitudinal direction of the opticalfiber 4. The fastening member 6 is located at the closest position (ascompared to the fastening member 7) to the laser diode 1 and ispreferably formed of an integral member with a clamping portion 28 forclamping the sleeve 3 and the optical fiber 4 at both sides. Thefastening member 6 preferably has a U-shaped crosssectional area.

[0073] FIGS. 6(a), 6(b), 6(c), and 6(d) depict various embodiments offastening members that can be used either as fastening member 6 or asfastening member 7. Note that the embodiments depicted in FIGS. 6(a) and6(b) are preferably used as fastening member 6, since the clampingportions 28 of these embodiments are configured to be positioned asclose as possible to the laser diode 1, which allows for more precisealignment between the laser diode 1 and the optical fiber 4. Note thatthe embodiments depicted in FIGS. 6(c) and 6(d) are preferably used asfastening member 7, since the positioning of the clamping portions 28are not as crucial. The integrated fastening member 7 depicted in FIG.6(c) can be used advantageously to have a predetermined position andwidth of clamping portions 28. The fastening member 7 depicted in FIG.6(d) has the separate portions 7 a and 7 b that can clamp together thesleeve 3 tightly. Additionally, using an embodiment as depicted in FIG.6(a) is preferred, since the fastening member of FIG. 6(a) includes ajoint portion 49 that prevents warping of the base 2 in the X-direction,as compared with the a fastening member as depicted in FIG. 6(d), whichhas two separate fastening parts each supporting one side of the opticalfiber 4.

[0074] During the manufacturing process, the optical fiber 4 is movedaround the second joint positions 11 in order for the optical fiber 4 tobe optically coupled with the laser diode 1. Accordingly, if theclamping portions 28 of the fastening member 6 are formed to have anarm-shape as depicted in FIG. 6(b), then the stress applied to thesecond joint positions 11 when the optical fiber 4 is moved togetherwith the sleeve 3 around the second joint positions 11 is dispersed asdeformation stress on the arm of the clamping portion 28, thereby makingit possible to reduce the effect of stress concentrations.

[0075] The present invention includes an optical system that generallyincludes a lens portion and an optical fiber. In the first embodimentthe lens portion 14 is a wedge-shaped anamorphic (rotationallyasymmetric) lens integrated into the optical fiber 4 and having astructure depicted in FIGS. 7(a) and 7(b). In detail, ridge line 14 ahas a cylindrical surface. As depicted in FIGS. 2, 3 and 7, a ridge line14 a at a tip end faces a laser beam emitting face 31 of the laser diode1 such that the ridge line 14 a is in the same plane as an active layerof the laser diode 1. Although the optical fiber 4 preferably has ananamorphic, wedge-shaped lens portion 14 as depicted in FIGS. 7(a) and7(b), the optical fiber 4 can alternatively be constructed as ananamorphic lens portion other than the wedge-shape portion, or as afiber lens portion other than an anamorphic lens portion.

[0076] The shape of the fiber lens is not limited to a wedge shape. Analternative embodiment of the lens portion 14 is a conical shaped,rotationally symmetric lens (similar in shape to an end of a sharpenedpencil) that is integrated into the optical fiber 4, as depicted inFIGS. 24(a) and 24(b). More specifically, the tip of the cone of such afiber lens has a spherical surface. The fiber lens depicted in FIGS.24(a) and 24(b) is commonly called “a tapered lens ended fiber” or “asemi-spherically lensed fiber.”

[0077] Alternatively, the optical system can be constructed to have adiscrete lens supported by the holder mounting member 5, an opticalisolator supported by the holder mounting member 5, a second lenssupported by the package 27, and an optical fiber supported by thepackage 27. (See the discussion for the third and fourth embodiments,which are depicted in FIGS. 16-21, for a similar configuration.) In thisconfiguration, the lens portion 14 is constructed as a discrete lensportion from the optical fiber 4 such that the discrete lens portion,the optical isolator, and the second lens are provided between the laserdiode 1 and the tip end of the optical fiber 4. In such a configuration,the optical isolator is preferably mounted using a material havingminimal magnetic properties, such as SUS 430, in order to reduceinterference with the optical isolator.

[0078] As depicted in FIG. 8(a), the laser diode 1 is preferably fixedon the heat sink 22 by, for example, AuSn or AuSi solder, and the heatsink 22 is fixed on the laser diode mounting member 8 by, for example,AuSn or AuSi solder. The heat sink 22 is preferably formed of materialof high thermal conductivity such as AlN or diamond. As depicted in FIG.8(b), the monitor photo diode carrier 39 is fixed on the laser diodemounting member 8 of the base 2 by soldering material 43. The monitorphoto diode carrier 39 is preferably formed mainly of alumina. An Auplating pattern 50 is formed on the surface of the monitor photo diodecarrier 39. The photo diode 9 is fixed on the plating pattern 50 bysoldering material 44, such as AuSn.

[0079]FIGS. 9 and 10 depict the internal components of a secondembodiment of the semiconductor laser diode module according to thepresent invention, where the thermo module 25 and the package 27 havebeen omitted. FIG. 11 is an exploded, perspective view of a base 2 ofthe second embodiment of the semiconductor laser diode module accordingto the present invention.

[0080] The second embodiment enjoys substantially the same advantages asthose of the above-described first embodiment. The feature of the secondembodiment that is different from the first embodiment is the uniqueshapes of the holder mounting member 5 and the laser diode mountingmember 8 which constitute the base 2. More specifically, in the secondembodiment the structural support members 15 are formed on both theholder mounting member 5 and the laser diode mounting member 8. Thestructural support members 15 are provided on both sides of the axialportion 33 connecting the laser beam emitting facet 31 of the laserdiode 1 and the laser beam receiving end 32 of the optical fiber 4 andon both sides of the fastening member 6 located closer to the laserdiode 1. The structural support members 15 are preferably formedintegrally with the holder mounting member 5 and integrally with thelaser diode mounting member 8.

[0081] The present invention is not limited to the above-describedembodiments but may take various forms. The following discussiondescribes various exemplary alternative configurations of the presentinvention.

[0082] The laser diode module according to the present inventionpreferably includes a thermo module 25 in order to control thetemperature of the laser diode 1, as described above. However, the laserdiode module of the present invention can be constructed without athermo module, such that the base 2 is supported by or integrated intothe bottom plate 26. Such a configuration is required, for example, inundersea application due to the suppression of electric powerconsumption.

[0083] The first and second embodiments depict structural supportmembers 15 that are formed as wall portions extending in thelongitudinal direction of the optical fiber and provided upright on anupper side of the holder mounting member 5 or the laser diode mountingmember 8. However, the configuration of the structural support members15 is not limited to the specific shape depicted in the figures, butrather can be configured in alternative shapes, for instance,rod-shaped, or angular shaped one, which are attached to the base 2 by,for example, adhesives or solder.

[0084] Furthermore, in each of the foregoing embodiments, the holdermounting member 5 of the base 2 is preferably provided to project in thelongitudinal direction of the optical fiber 4 from the end portion onthe optical fiber mounting side of the laser diode mounting member 8.However, it is not necessary to provide the holder mounting member 5 ofthe base 2 so as to project from the laser diode mounting member 8 asdescribed above. Other configurations can be used as will be readilyapparent to one of skill in the art based upon the teaching set forthherein.

[0085] In each of the foregoing embodiments, the laser diode mountingmember 8 preferably has a reinforcement portion 20 formed under thefastening member 6 located on the closest side to the laser diode 1.Alternatively, it is possible to dispense with the reinforcement portion20. However, since the reinforcement portion 20 is provided to suppressthe vibration of the holder mounting member 5 in the Y-direction of thedrawings, it is preferable to provide the reinforcement portion 20.Furthermore, the configuration of the reinforcement portion 20 is notlimited to any particular shape, but rather may be selected as desired.For instance, the reinforcement portion 20 may take a structure having atapered surface, as indicated by phantom lines A in FIG. 2.

[0086] Although the laser diode mounting member 8 and the bottom plate26 of the package 27 of the preferred embodiments are made of the samematerial to have the same thermal expansion coefficient, it is possibleto use different materials for the laser diode mounting member 8 and thebottom plate 26. However, in this configuration it is preferable if thethermal expansion coefficients of the different materials aresubstantially the same.

[0087] The present invention provides a structure that advantageouslyreduces any degradation in the optical characteristics, i.e. the opticalcoupling efficiency of the laser diode module, due to the changes in theambient temperature of the module. As described earlier with respect toFIGS. 7(a) and 7(b), the optical fiber 4 of the first embodiment has thewedge-shaped lens portion 14 with the ridge line 14 a at a tip end inparallel with the X-Z plane. The optical coupling between the lensportion 14 of the optical fiber 4 and the laser diode 1 is susceptibleto adverse effects of positional displacement, in particular, in theY-direction if bending of the module occurs, as seen with respect to therelated embodiment depicted in FIGS. 12(a), 12(b), 13(a), 13(b), 14(a),and 14(b).

[0088] When the base 2 is warped along the longitudinal direction of theoptical fiber 4, the degradation in optical coupling efficiency betweenthe laser diode 1 and the optical fiber 4 is likely to significantlyoccur. However, in accordance with the first embodiment of the presentinvention, the warping of the base 2 along the longitudinal direction ofthe optical fiber 4 is suppressed by the structural support members 15,thereby the stability of the optical coupling efficiency between thelaser diode 1 and the optical fiber 4.

[0089] In the first and second embodiments, since the light emitted fromthe laser diode 1 is introduced from the tip end side of the opticalfiber 4 into the optical fiber 4, it is important to suppress thepositional displacement between the laser diode 1 and a laser beamreceiving end 32 of the optical fiber 4. It is therefore important tosuppress the warping of the base 2 at the axial portion 33.Additionally, a displacement in the fastened position of the sleeve 3 bythe fastening member 6 will cause a greater degradation in couplingefficiency as compared to that by the fastening member 7, which islocated further from the laser diode 1 than the fastening member 6.Therefore, it is important to suppress the warping of the base 2 in theregion where the fastening member 6 is arranged. The present inventionachieves such an advantageous structure.

[0090]FIG. 15 is a chart representing monitor tracking error based uponambient temperature changes in the semiconductor laser diode module ofthe related art and of the present invention. The monitor tracking erroris defined as ΔIm=(Im(T)−Im(25° C.))/Im(25° C.). In the laser diodemodule according to the present invention, since the warping of the baseis suppressed, the sinusoidal change in the back-facet monitor currentdue to the change in ambient temperature is suppressed. As depicted inFIG. 15, the tracking error (ΔIm) of the laser diode module of thepresent invention appears to change with a longer period than therelated art laser diode module, which demonstrates that the variouswarping prevention means of the present invention function to preventthe displacement of the fiber-end with respect to the laser diode.

[0091] A third embodiment of the present invention will be hereinafterdescribed with reference to FIGS. 17-21.

[0092] The third embodiment is an example of a system coupling adiscrete lens to a laser diode where the semiconductor laser diodemodule has a wavelength 1480 nm band that is applied to an opticalamplifier of a submarine system or a metro system. Obviously, it isdifficult to frequently replace a semiconductor laser diode moduleapplied to an optical amplifier of a submarine cable after installingit, therefore it is necessary to realize long term reliability of thesemiconductor laser diode module. Accordingly, the laser diode modulemust be constructed to prevent optical coupling dislocation between thelaser diode and the discrete lens due to the deflection of the base overa long period of time. Deflection of the base can be cause by variousfactors, such as distortion of the package due to screwing when thesemiconductor laser diode module is fixed to a printed board, warp ofthe various portions of the module due to difference in temperature ofcontacting portions, and deflection due to a difference of thermalexpansion coefficient between contacting portions.

[0093] The third embodiment of the present invention has been devised inview of the above and other concerns. The present invention provides asemiconductor laser diode module with high long term reliability whichcan satisfactorily maintain optical coupling between a luminous elementsuch as a laser diode and a discrete lens.

[0094] As depicted in FIGS. 17 and 18, the semiconductor laser diodemodule of the third embodiment has a laser diode 101, and a discretelens 114 optically coupled to the laser diode 101. The discrete lens 114and the laser diode 101 are mounted on a base 102. The base 102 has alaser diode mounting member 108 as a laser diode mounting section, and aholder mounting member 105 for mounting the discrete lens 114. The base102, the laser diode 101 and the discrete lens 114 are contained withina package 127. The base 102 is directly fixed to a bottom plate 126 ofthe package 127, and a laser diode mounting member 108 is arranged incontact with the package bottom plate 126.

[0095] A laser diode bonding portion 121 is provided on an upper side ofthe laser diode mounting member 108 to form a laser diode mountingregion. The laser diode 101 is fixed to the laser diode bonding portion121 via a heat sink 122. In addition, a thermistor 129 is preferablyfixed to a fixing section 148 provided on the laser diode bondingportion 121. On the rear side of the laser diode bonding portion 121 ofthe laser diode mounting member 108, a photodiode 109 for monitoring theoutput of the laser diode 101, which is attached by chip carrier, isarranged in a position 147 shown by hatching in FIG. 17.

[0096] In the third embodiment, the laser diode mounting member 108 ispreferably formed of CuW20 (a weight ratio is Cu 20% and W 80%), whichis a Cu—W alloy having a high thermal conductivity preferably of 150W/mK or more. Therefore, in the third embodiment, heat generated by thelaser diode 101 can be efficiently transferred to the bottom plate 126.

[0097] The holder mounting member 105 is arranged on a front side of thelaser diode bonding portion 121 of the laser diode mounting member 108.The holder mounting member 105 is fixed to the laser diode mountingmember 108 by a brazing section 146 shown by hatching in FIG. 19. Theholder mounting member 105 is substantially U-shaped along across-sectional view perpendicular to an optical axis of the laser diode101 by vertically forming wall sections 105 b, as depicted in FIG. 20.The wall sections 105 b extend in the direction of the optical axis (theoptical axis direction of the laser diode 101) on both sides of a basesection 105 a. Additionally, arm sections 105 e are protrudingly formedby the rear end part of the side wall section 105 b to the rear side inthe direction of the optical axis in the holder mounting member 105,which increases a contacting area of the brazing section 146 and, at thesame time, prevents warp of the base 102. A cross-sectional shape of aconnection configuration between the arm sections 105 e and the laserdiode mounting member 108 also is substantially U-shaped along a crosssection taken perpendicular to the optical axis of the laser diode 101.The above configuration provides a deflection preventing means in whichthe base is substantially U-shaped in a cross section perpendicular tothe optical axis of the laser diode so as to enclose at least the partwhere the laser diode and the discrete lens are optically coupled.Therefore, the above-mentioned deflection preventing means can moresurely, with a simple configuration, prevent or restrain a decrease inthe efficiency of the optically coupling between the laser diode and thediscrete lens due to deflection of the base.

[0098] In addition, protruding wall sections 105 c and 105 d areprotrudingly formed in the direction perpendicular to the optical axisdirection of the laser diode 101 from the side wall section 105 b in theholder mounting member 105, and are configured such that fasteningmembers 106 are inserted between them.

[0099] As described above, the base 102 is substantially U-shaped in across-sectional view taken perpendicular to the optical axis of thelaser diode 101 so as to enclose at least a portion of the laser diodemodule where the laser diode 101 and the discrete lens 114 are opticallycoupled. Such a base configuration having a substantially U-shaped crosssection is very strong against deflection, and forms deflectionpreventing means for preventing deflection of the base 102 at the partwhere at least the laser diode 101 and the discrete lens 114 areoptically coupled.

[0100] As shown in FIG. 17, the discrete lens 114 includes a lens holder124. The lens holder 124 is fixed to the holder mounting member 105 ofthe base 102 via fastening members or fastening means 106. The lensholder 124 and the fastening members 106 preferably have thermalexpansion coefficient close to that of a glass material forming thediscrete lens 114, and are preferably formed by Kovar®, which is anFe-Ni-Co alloy having satisfactory laser-welding properties. Thefastening members 106 can be configured in shapes as described in thefirst and second embodiments of the present invention (see FIGS. 6(a),6(b), 6(c), and 6(d)).

[0101] A first joint position or laser-welded section 110 is preferablyformed by laserwelding the holder mounting member 105 of the base 102and the fastening member 106, and a second joint position orlaser-welded section 111 is preferably formed by laser-welding thefastening member 106 and the lens holder 114. The first joint position110 and the second joint position 112 are preferably formed atsubstantially a same height in a direction perpendicular to the baseplate 126 of the package 127.

[0102] In addition to the discrete lens 114, the optical system of thethird embodiment includes an optical isolator 130, a second lens 153,and an optical fiber 157. The optical isolator 130 is provided on theholder mounting member 105. The optical isolator is configured to allowlight that passed through the discrete lens 114 to pass and configuredto block light returning to the laser diode 101 side. A third jointposition or laser-welded section 112 is preferably formed bylaser-welding the optical isolator 130 and the holder mounting member105. The third joint position 112 is preferably formed at substantiallythe same height as the first and the second joint positions 110 and 111in the direction perpendicular to the base plate 126 of the package 127.

[0103]FIG. 21 shows the positional relationship among the holdermounting member 105, the fastening members 106, and the optical isolator130 along line XX-XX in FIG. 17. As shown in FIG. 21, even if the base 2tends to warp in a α direction (a direction in which both ends in theoptical axis direction displace upward), the warp of the holder mountingmember 105 in the α direction is restrained because the protruding wallsection 105 d exists between the fastening member 106 and the opticalisolator 130. Additionally, even if the module tends to warp in a βdirection (a direction in which both ends in the optical axis directiondisplace downward), the warp in the β direction is restrained becausethe fastening member 106 is fixed to the protruding wall sections 105 cand 105 d by laser-welding in the optical axis direction, and theoptical isolator 130 is fixed to the wall section 105 b.

[0104] In particular, since the fastening member 106 and the protrudingwall sections 105 c and 105 d are laser-welded on surfaces opposing eachother that are formed in the direction perpendicular to the optical axisdirection, only tensile stress or compressive stress is applied andshearing stress is not applied against the warp in the α and the βdirections. Therefore, subsidiary fracture of a laser-welded point canbe more effectively prevented. From this point of view, the opticalisolator 130 and the protruding wall section 105 d can be configuredsuch that they are joined, for example by laser-welding, at a fourthjoint position designated by the reference numeral 110′.

[0105] In addition, the height of an upper surface 145 of the wallsection 105 b in the holder mounting member 105 substantially coincideswith the optical axis of the laser diode 101. Therefore, the height ofthe first, the second and the third joint positions 110, 111 and 112substantially coincide with that of the optical axis of the laser diode101. Thus, since the optical axis of the discrete lens 114 and theoptical isolator 130 are positioned at this height, positionaldislocation due to warping of the package and the base 102 can berestrained.

[0106] The holder mounting member 105 is made of a material havingbeneficial laserwelding characteristics, for example, the holdermounting member 105 preferably has a thermal conductivity of 50 W/mK orless thereby providing beneficial laser-welding characteristics for theholder mounting member 105 and the fastening members 106. In addition,the holder mounting member 105 is made of a material having deflectionpreventing properties, for example, the holder mounting member 105 ismade of a material preferably having a Young's modulus of 15×10³ kg/mm²or more in order to prevent deflection. Moreover, the holder mountingmember 105 is preferably made of a material having weak magnetism(preferably without magnetism) so as not to damage the magnetism of theoptical isolator 130 that is mounted thereon. For example, the holdermounting member 105 can be formed of SUS 430, since SUS 430 has athermal conductivity of 26.4 W/mK, a Young's modulus of 20.4×10³ kg/m²,and magnetism that is weak. Accordingly, since SUS 430 has low thermalconductivity, favorable laser-welding property is realized, and sinceSUS 430 has a high Young's modulus, a deflection preventive effect canbe realized. Moreover, since SUS 430 has weak magnetism, magnetism ofthe optical isolator 130 is not damaged. Thus, an excellentsemiconductor module having both favorable productivity and long termreliability can be realized.

[0107] As shown in FIG. 18, a through hole 151 is formed in the sidewall of the package 127, and a light transmitting plate 152 for sealingthe package is fixed to this through hole 151. In addition, a holder 154to which a second lens 153 is fixed is inserted to be fixed to thethrough hole 151, and a ferule holder 155 is fixed to the one end side(right side of the figure) of this holder 154. A ferule 156 is fixed tothe ferule holder 155, and an optical fiber (single mode optical fiber)157 is inserted to be fixed to the ferule 156. In the third embodiment,a laser beam emitted from the laser diode 101 is optically coupled tothe discrete lens 114 and incident on the optical isolator 130 throughthe discrete lens 114. Then, the light transmitted through the opticalisolator 130 is collected on the incident side of the optical fiber 157by the second lens 153, and is transmitted for a desired applicationthrough the optical fiber 157.

[0108] According to the third embodiment, since the base 102 mountingthe laser diode 101 and the discrete lens 114 is formed by the laserdiode mounting member 108 and the holder mounting member 105, and sincethe holder mounting member 105 is substantially U-shaped in the crosssection perpendicular to the optical axis of the laser diode 101 and isto be fixed on the laser diode mounting member 108, then the holdermounting member 105 forms means for preventing deflection of the base102, and deflection of the base 102 can be restrained by the deflectionpreventing means.

[0109] According to the third embodiment, since the upper surface 145 ofthe holder mounting member 105 is made to substantially coincide withthe height of the optical axis of the laser diode 101, a decrease in theefficiency of optically coupling the laser diode 101 and the discretelens 114 due to deflection of the base 102 can be surely restrained, anda semiconductor laser diode module with high long term reliability canbe realized. In addition, since the first joint position 110 and thesecond joint position 111 are formed at substantially the same height(on the identical surface), then optical axis dislocation of thediscrete lens 114 due to deflection of the base 102 is prevented.Moreover, since the optical isolator 130 is arranged on the holdermounting member 105 of the base 102, and the height of the third jointposition 112 is made substantially the same as that of the first and thesecond joint positions, then dislocation of the optical isolator 130 asa result of deflection of the base 102 can be also restrained.

[0110] Thus, according to the third embodiment, a decrease in theefficiency of optically coupling the laser diode 101 and the discretelens 114 can be more surely restrained, and a semiconductor laser diodemodule with higher long term reliability can be realized.

[0111] The present invention is not limited to the above-mentionedembodiment, and various alternative embodiments may be adopted. Forexample, whereas in the third embodiment the base 102 is directly fixedon the bottom plate 126 of the package 127, a fourth embodiment can beprovided with a thermo-module 125 on the bottom plate 126 of the package127 for fixing the base 102 thereon, as depicted in FIG. 22.Accordingly, the temperature of the laser diode can be appropriatelycontrolled by the thermo-module.

[0112] Moreover, whereas the base 102 in the third embodiment isconfigured to have both a holder mounting member 105 and a laser diodemounting member 108, the base 102 may be formed by as a unitary memberhaving a holder mounting member for mounting the discrete lens 114.

[0113] Moreover, whereas the laser diode module of the third embodimentis formed by fixing an optical isolator 130 on the holder mountingmember 105, the optical isolator 130 can be fixed to the package by astructure other than the holder mounting member 105, or the laser diodemodule may be formed without an optical isolator.

[0114] Moreover, whereas the discrete lens 114 of the third embodimentis used as a collimate lens, alternatively it may be used as a condenserlens to couple light to the optical fiber 157 without using the secondlens 153.

[0115] It should be noted that the exemplary embodiments depicted anddescribed herein set forth the preferred embodiments of the presentinvention, and are not meant to limit the scope of the claims hereto inany way. The various embodiments of the present invention providenumerous advantageous configurations, some of which are described below.

[0116] According to a first aspect of the present invention, since thebase is formed by the laser diode mounting member contacted and disposedon the thermo module and by the holder mounting member on the upper sidethereof, with the laser diode mounting member being formed of materialhaving a thermal expansion coefficient in a range between a thermalexpansion coefficient of the holder mounting member and a thermalexpansion coefficient of the base side plate member of the thermomodule, the present invention advantageously suppresses the warping ofthe base caused by the temperature change in the environmentalcircumstances of the semiconductor laser diode module in comparison withthe related art module. Accordingly, the present inventionadvantageously suppresses the degradation in optical coupling efficiencybetween the laser diode and the optical fiber due to the temperaturechange of the environmental circumstances of the semiconductor laserdiode module.

[0117] According to a second aspect of the invention, since the base isformed by the laser diode mounting member contacted and disposed on thethermo module and by the holder mounting member, with the thermalexpansion coefficients of the laser diode mounting member and the bottomplate of the package being substantially equal to each other, the samemagnitude of stress is applied on both upper and lower sides of thethermo module when the temperature change of the semiconductor laserdiode module is generated. Therefore, the present inventionadvantageously offsets the warping of the thermo module and suppressesthe degradation in optical coupling efficiency between the laser diodeand the optical fiber due to the ambient temperature change.

[0118] According to a third aspect of the invention, since a first jointposition obtained by laser-welding together the holder mounting memberand the fastening members of the sleeve for holding the optical fiberand a second joint position obtained by laser-welding together thefastening members and the sleeve are formed to be at substantially thesame height level in a direction perpendicular to a bottom plate of thepackage, even if warping is generated in the base to some extent, thereis no significant positional displacement of the sleeve corresponding tothe warping. Accordingly, the present invention advantageouslysuppresses the degradation in optical coupling efficiency between thelaser diode and the optical fiber.

[0119] According to a fourth aspect of the invention, since a structuralsupport member for preventing the warping of the base is provided on thebase in a longitudinal direction of the optical fiber on at least oneside of the optical fiber, the warping of the base is suppressed by thestructural support members. Accordingly, the present inventionadvantageously suppresses the degradation in optical coupling efficiencybetween the laser diode and the optical fiber.

[0120] According to a fifth aspect of the invention, since a structuralsupport member is provided on at least one side of an axial portionconnecting a laser beam emitting facet of the laser diode and a laserbeam receiving end of the optical fiber, warping at the axial portion issuppressed and the degradation in optical coupling efficiency betweenthe laser diode and the optical fiber is efficiently suppressed.Accordingly, the present invention advantageously suppresses thedegradation in optical coupling efficiency between the laser diode andthe optical fiber.

[0121] According to a sixth aspect of the invention, since a structuralsupport member is provided on at least one side of the fastening memberlocated on the closest side to the laser diode (i.e., in a region alongthe longitudinal direction of the optical fiber of the holder mountingmember including at least one side), warping of the base in the regionof the fastening member that is most likely to affect the degradation inoptical coupling efficiency between the laser diode and the opticalfiber is suppressed.

[0122] According to a seventh aspect of the invention, since astructural support member is formed integrally with the holder mountingmember, it is possible to avoid a reduction in mechanical strength dueto the connection between a structural support member and a discreteholder mounting member. Thus, it is possible to effectively prevent thewarping of the base by the structural support members, and toeffectively suppress the degradation in optical coupling efficiencybetween the laser diode and the optical fiber.

[0123] According to an eighth aspect of the invention, since thestructural support member is preferably formed with a wall portionextending in a longitudinal direction of the optical fiber, and providedupright at least on an upper side of the holder mounting member, it ispossible to provide means for effectively suppressing the warping of thebase with a simple structure. Accordingly, the present inventionadvantageously suppresses the degradation in optical coupling efficiencybetween the laser diode and the optical fiber.

[0124] According to a ninth aspect of the invention, since the fasteningmember for supporting and fastening the optical fiber in the closestside to the laser diode is formed of an integral part provided with aclamping portion for clamping both sides of the optical fiber, it ispossible to suppress the warping of the base in the horizontal directionintersecting with the longitudinal direction of the optical fiber incomparison with a case where separate fastening members support eachside of the optical fiber. Accordingly, the present inventionadvantageously suppresses the degradation in optical coupling efficiencybetween the laser diode and the optical fiber.

[0125] According to a tenth aspect of the invention, since the base isprovided to project in the longitudinal direction of the optical fiberfrom end portion of the thermo module on the optical fiber mountingside, it is possible to suppress the phenomenon that the portion that isout of contact with the thermo module (i.e., the projection portion ofthe base) is subjected to the adverse effect of the warping of thethermo module. Thus, a fastening member of the optical fiber is mountedin this region to thereby make it possible to effectively suppress thedegradation in optical coupling efficiency between the laser diode andthe optical fiber.

[0126] According to an eleventh aspect of the invention, since theholder mounting member of the base is provided to project in thelongitudinal direction of the optical fiber from the end portion of thelaser diode mounting member on the optical fiber mounting side, it ispossible to suppress the phenomenon that this portion is subjected tothe adverse effect of the warping of the laser diode mounting member.Thus, a fastening member of the optical fiber is mounted in thisprojected region to thereby make it possible to effectively suppress thedegradation in optical coupling efficiency between the laser diode andthe optical fiber.

[0127] According to a twelfth aspect of the invention, since the laserdiode mounting member of the base has a reinforcement portion formedunder the fastening member located in the closest position to the laserdiode, even if the vibration in the direction perpendicular to thepackage bottom plate is applied to the holder mounting member, anypivoting caused by the vibration will be farther from the laser diodethan the fastening member. Additionally, the lower surface of thereinforcement portion is out of contact with the thermo module wherebyit is possible to suppress the adverse effect of the warping of thethermo module against the reinforcement portion.

[0128] According to a thirteenth aspect of the invention, since theholder mounting member, the fastening members and the structural supportmembers are preferably made of Kovar® or a similar material, it ispossible to manufacture a semiconductor laser diode module with highworkability/weldability. Additionally, Kovar® advantageously hassubstantially the same thermal expansion coefficient as that of theoptical fiber, and thus adverse effects on the optical fiber due to thedifference in thermal expansion coefficient between the optical fiber,and the holder mounting member and the structural support member aresuppressed.

[0129] Numerous modifications and variations of the present inventionare possible in light of the above teachings. It is therefore to beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

What is claimed is:
 1. A laser diode module comprising: a laser diode;an optical system including an optical fiber and a lens portion, saidoptical system being configured to receive and transmit a beam emittedfrom said laser diode through said lens portion to said optical fiberalong an optical axis; a holder configured to receive a portion of saidoptical system; a base having a holder mounting member and a fasteningmember, said holder being mounted to said fastening member at a firstjoint position, said fastening member being mounted to said holdermounting member at a second joint position; and a bottom plateconfigured to support said base, wherein said first joint position andsaid second joint position are located at substantially a same distancefrom said bottom plate.
 2. The laser diode module according to claim 1,wherein said holder is configured to receive a portion of said opticalfiber.
 3. The laser diode module according to claim 1, wherein said lensportion is a discrete lens supported by said holder mounting member. 4.The laser diode module according to claim 3, wherein said discrete lensis mounted within said holder.
 5. The laser diode module according toclaim 3, wherein: said optical system further comprises a second lens;and said laser diode module further comprises a package including saidbottom plate, said package being configured to support said second lensand said optical fiber.
 6. The laser diode module according to claim 3,wherein: said optical system further comprises an optical isolatorsupported by said holder mounting member; and said optical system isconfigured to receive and transmit the beam emitted from said laserdiode through said discrete lens and said optical isolator to saidoptical fiber along said optical axis.
 7. The laser diode moduleaccording to claim 6, wherein: said optical isolator is mounted to saidholder mounting member at a third joint position; and said first jointposition, said second joint position, and said third joint positionbeing located at substantially a same distance from said bottom plate.8. The laser diode module according to claim 6, wherein: said opticalisolator is mounted to said holder mounting member at a fourth jointposition, said third joint position being located on a first surface ofsaid optical isolator and said fourth joint position being located on asecond surface of said optical isolator, said first surface beingsubstantially perpendicular in orientation to said second surface; andsaid first joint position, said second joint position, said third jointposition, and said fourth joint position being located at substantiallya same distance from said bottom plate.
 9. The laser diode moduleaccording to claim 1, wherein: said holder is mounted to said fasteningmember at a plurality of first joint positions; said fastening member ismounted to said holder mounting member at a plurality of second jointpositions; and said plurality of first joint positions and saidplurality of second joint positions are coplanar.
 10. The laser diodemodule according to claim 9, wherein said plurality of first jointpositions include at least one joint position on a first side of saidholder and at least one joint position on a second side of said holderopposite said first side.
 11. The laser diode module according to claim9, wherein said plurality of second joint positions include at least onejoint position on a first side of said fastening member and at least onejoint position on a second side of said fastening member opposite saidfirst side.
 12. The laser diode module according to claim 9, whereinsaid plurality of first joint positions are symmetrically oriented onopposing sides of said holder about said optical axis.
 13. The laserdiode module according to claim 9, wherein said plurality of secondjoint positions are symmetrically oriented on said opposing sides ofsaid fastening member about said optical axis.
 14. The laser diodemodule according to claim 1, wherein said holder is mounted to saidfastening member at said first joint position by laser welding, and saidfastening member is mounted to said holder mounting member at saidsecond joint position by laser welding.
 15. The laser diode moduleaccording to claim 1, wherein said base includes a plurality offastening members received within a corresponding plurality of recessedportions on said holder mounting member.
 16. The laser diode moduleaccording to claim 1, wherein said fastening member is coupled to saidholder at a location adjacent said lens portion of said optical system.17. The laser diode module according to claim 1, further comprising athermo module coupling said base to said bottom plate, said thermomodule comprising a first plate member attached to a portion of saidbase, a peltier element attached to said first plate member, and asecond plate member attached to said peltier element and said bottomplate.
 18. The laser diode module according to claim 1, wherein saidfirst joint position and said second joint position are coplanar along aplane extending through a longitudinal axis of said optical fiber.
 19. Alaser diode module comprising: a laser diode having an active layer; anoptical system including an optical fiber and a lens portion, saidoptical system being configured to receive and transmit a beam emittedfrom said laser diode through said lens portion to said optical fiberalong an optical axis; a holder configured to receive a portion of saidoptical system; and a base having a holder mounting member and afastening member, said holder being mounted to said fastening member ata first joint position, said fastening member being mounted to saidholder mounting member at a second joint position, said first jointposition and said second joint position are coplanar with said activelayer of said diode.
 20. The laser diode module according to claim 19,wherein said holder is configured to receive a portion of said opticalfiber.
 21. The laser diode module according to claim 19, wherein saidlens portion is a discrete lens supported by said holder mountingmember.
 22. The laser diode module according to claim 21, wherein saiddiscrete lens is mounted within said holder.
 23. The laser diode moduleaccording to claim 21, wherein: said optical system further comprises asecond lens; and said laser diode module further comprises a packageincluding a bottom plate, said package being configured to support saidsecond lens and said optical fiber.
 24. The laser diode module accordingto claim 21, wherein: said optical system further comprises an opticalisolator supported by said holder mounting member; and said opticalsystem is configured to receive and transmit the beam emitted from saidlaser diode through said discrete lens and said optical isolator to saidoptical fiber along said optical axis.
 25. The laser diode moduleaccording to claim 24, wherein: said optical isolator is mounted to saidholder mounting member at a third joint position; and said first jointposition, said second joint position, and said third joint position arecoplanar with said active layer of said diode.
 26. The laser diodemodule according to claim 24, wherein: said optical isolator is mountedto said holder mounting member at a fourth joint position, said thirdjoint position being located on a first surface of said optical isolatorand said fourth joint position being located on a second surface of saidoptical isolator, said first surface being substantially perpendicularin orientation to said second surface; and said first joint position,said second joint position, said third joint position, and said fourthjoint position are coplanar with said active layer of said diode. 27.The laser diode module according to claim 19, wherein: said holder ismounted to said fastening member at a plurality of first jointpositions; and said fastening member is mounted to said holder mountingmember at a plurality of second joint positions.
 28. The laser diodemodule according to claim 27, wherein said plurality of first jointpositions include at least one joint position on a first side of saidholder and at least one joint position on a second side of said holderopposite said first side.
 29. The laser diode module according to claim27, wherein said plurality of second joint positions include at leastone joint position on a first side of said fastening member and at leastone joint position on a second side of said fastening member oppositesaid first side.
 30. The laser diode module according to claim 27,wherein said plurality of first joint positions are symmetricallyoriented on opposing sides of said holder about said optical axis. 31.The laser diode module according to claim 27, wherein said plurality ofsecond joint positions are symmetrically oriented on said opposing sidesof said fastening member about said optical axis.
 32. The laser diodemodule according to claim 19, wherein said holder is mounted to saidfastening member at said first joint position by laser welding, and saidfastening member is mounted to said holder mounting member at saidsecond joint position by laser welding.
 33. The laser diode moduleaccording to claim 19, wherein said base includes a plurality offastening members received within a corresponding plurality of recessedportions on said holder mounting member.
 34. The laser diode moduleaccording to claim 19, wherein said fastening member is coupled to saidholder at a location adjacent said lens portion of said optical system.35. The laser diode module according to claim 19, further comprising: abottom plate configured to support said base; and a thermo modulecoupling said base to said bottom plate, said thermo module comprising afirst plate member attached to a portion of said base, a peltier elementattached to said first plate member, and a second plate member attachedto said peltier element and said bottom plate.
 36. The laser diodemodule according to claim 19, wherein said first joint position and saidsecond joint position are coplanar along a plane extending through saidoptical axis.
 37. A laser diode module comprising: a laser diode; anoptical system including an optical fiber and a lens portion, saidoptical system being configured to receive and transmit a beam emittedfrom said laser diode through said lens portion to said optical fiberalong an optical axis; a holder configured to receive a portion of saidoptical system; and a base having a holder mounting member and afastening member, said holder being mounted to said fastening member ata plurality of first joint positions, said fastening member beingmounted to said holder mounting member at a plurality of second jointpositions, said plurality of first joint positions and said plurality ofsecond joint positions are coplanar.
 38. The laser diode moduleaccording to claim 37, wherein said holder is configured to receive aportion of said optical fiber.
 39. The laser diode module according toclaim 37, wherein said lens portion is a discrete lens supported by saidholder mounting member.
 40. The laser diode module according to claim39, wherein said discrete lens is mounted within said holder.
 41. Thelaser diode module according to claim 39, wherein: said optical systemfurther comprises a second lens; and said laser diode module furthercomprises a package including a bottom plate, said package beingconfigured to support said second lens and said optical fiber.
 42. Thelaser diode module according to claim 39, wherein: said optical systemfurther comprises an optical isolator supported by said holder mountingmember; and said optical system is configured to receive and transmitthe beam emitted from said laser diode through said discrete lens andsaid optical isolator to said optical fiber along said optical axis. 43.The laser diode module according to claim 42, wherein: said opticalisolator is mounted to said holder mounting member at a plurality ofthird joint positions; and said plurality of first joint positions, saidplurality of second joint positions, and said plurality of third jointpositions are coplanar.
 44. The laser diode module according to claim42, wherein: said optical isolator is mounted to said holder mountingmember at a plurality of fourth joint positions, said plurality of thirdjoint positions being located on a first surface of said opticalisolator and said plurality of fourth joint positions being located on asecond surface of said optical isolator, said first surface beingsubstantially perpendicular in orientation to said second surface; andsaid plurality of first joint positions, said plurality of second jointpositions, said plurality of third joint positions, and said pluralityof fourth joint positions are coplanar.
 45. The laser diode moduleaccording to claim 37, wherein said plurality of first joint positionsand said plurality of second joint positions are coplanar along a planeextending through said optical axis.
 46. A semiconductor laser diodemodule comprising: a laser diode; an optical system including an opticalfiber and a lens portion, said optical system being configured toreceive and transmit a beam emitted from said laser diode through saidlens portion to said optical fiber along an optical axis; a holderconfigured to receive a portion of said optical system; a fasteningmeans for fixing said portion of said optical system by supporting andclamping said holder on sides thereof; a base configured to support saidfastening means and said laser diode, said base including a fasteningmeans mounting member configured to mount said fastening means; and abottom plate configured to support said base, said fastening means, saidholder, said optical system, and said laser diode, wherein a firstwelding position is obtained by welding said fastening means to saidfastening means mounting member and a second welding position isobtained by welding said fastening means and said holder, and whereinsaid first welding position and said second welding position are atsubstantially a same height in a direction perpendicular to said bottomplate.
 47. The semiconductor laser diode module according to claim 46,wherein said holder is configured to receive a portion of said opticalfiber.
 48. The semiconductor laser diode module according to claim 46,wherein said lens portion is a discrete lens supported by said fasteningmeans mounting member.
 49. The semiconductor laser diode moduleaccording to claim 48, wherein said discrete lens is mounted within saidholder.
 50. The semiconductor laser diode module according to claim 48,wherein: said optical system further comprises a second lens; and saidsemiconductor laser diode module further comprises a package includingsaid bottom plate, said package being configured to support said secondlens and said optical fiber.
 51. The semiconductor laser diode moduleaccording to claim 48, wherein: said optical system further comprises anoptical isolator supported by said fastening means mounting member; andsaid optical system is configured to receive and transmit the beamemitted from said laser diode through said discrete lens and saidoptical isolator to said optical fiber along said optical axis.
 52. Thesemiconductor laser diode module according to claim 51, wherein: saidoptical isolator is mounted to said fastening means mounting member at athird welding position; and said first welding position, said secondwelding position, and said third welding position are at substantially asame height in a direction perpendicular to said bottom plate.
 53. Thesemiconductor laser diode module according to claim 52, wherein: saidoptical isolator is mounted to said fastening means mounting member at afourth welding position, said third welding position being located on afirst surface of said optical isolator and said fourth welding positionbeing located on a second surface of said optical isolator, said firstsurface being substantially perpendicular in orientation to said secondsurface; and said first welding position, said second welding position,said third welding position, and said fourth welding position are atsubstantially a same height in a direction perpendicular to said bottomplate.
 54. The semiconductor laser diode module according to claim 46,further comprising: a thermo module mounted on said bottom plate, saidbase being mounted on said thermo module; and a package configured toaccommodate said laser diode, said optical system, said holder, saidfastening means, said base and said thermo module, said packageincluding said bottom plate.
 55. The semiconductor laser diode moduleaccording to claim 46, wherein said base projects in a longitudinaldirection of said optical fiber from an end portion on an optical fibermounting side of said thermo module.
 56. The semiconductor laser diodemodule according to claim 55, wherein: said base includes a laser diodemounting member configured to mount said laser diode at a laser diodemounting region and disposed on said thermo module; said fastening meansmounting member is disposed in a position other than said laser diodemounting region; and said fastening means mounting member projects insaid longitudinal direction of said optical fiber from an end portion onan optical fiber mounting side of said laser diode mounting member. 57.The semiconductor laser diode module according to claim 56, wherein saidlaser diode mounting member has a reinforcement portion configured tomechanically reinforce said fastening means located in a closestposition to said laser diode, and wherein said reinforcement portion hasa lower surface that is out of contact with said thermo module.
 58. Thesemiconductor laser diode module according to claim 46, wherein saidlens portion has a fiber lens formed on said optical fiber, and whereinsaid fiber lens has a tip end side that is arranged opposite a lightemitting facet of said laser diode.
 59. The semiconductor laser diodemodule according to claim 58, wherein said fiber lens is an anamorphiclens.
 60. The semiconductor laser diode module according to claim 46,wherein said fastening means mounting member is formed of an Fe-Ni-Coalloy.
 61. The semiconductor laser diode module according to claim 46,wherein said fastening means is formed of an Fe-Ni-Co alloy.